You want to root for “Hello, I Must Be Going,” a soft and heartfelt little film built on the backs of two all-in performances, but the film’s lack of credibility and flabby craft keep defeating your goodwill.

Todd Louiso, the sometime actor who previously directed “Love, Liza,” is empathetic enough with his actors to draw good work from them. But the screenplay by newcomer Sarah Koskoff is wan and sometimes even silly, and Louiso never finds a tone to sell it.

The fault isn’t with his stars. Melanie Lynskey is quite good as Amy, a newly divorced thirtysomething forced to move in with her parents in her childhood suburban home. Listless, lifeless and self-pitying, she only emerges through the most unlikely of avenues: an affair with Jeremy (Christopher Abbott), the 19-year-old son of her dad’s business acquaintance. As she navigates the various passages of life, she must endure the scorn of her mother (Blythe Danner), who dreams of a life that hasn’t quite come to her.

Danner is, in fact, the best thing in the picture: brittle and frank and cool toward a daughter who has flat-out disappointed her. She’s terrific. And you can’t help but feel at least some sympathy toward Amy, at least at the start, particularly as embodied by the winning Lynskey. But the script’s contrivances and the director’s lax handling aren’t enough to hold you.